The invention relates to a surgical instrument for introducing intervertebral implants into the intervertebral space between adjacent vertebral bodies.
Intervertebral implants are inserted in place of a removed disk into the intervertebral space between two adjacent vertebral bodies in order to maintain the distance between the latter and to enable the two adjacent vertebral bodies to stabilize through bone fusion after removal of the disk.
Introducing such an, as a rule, plate- or cage-shaped implant into the intervertebral space may be difficult because after removal of the disk the vertebral bodies are pressed towards one another by the action of the muscles. It is therefore necessary to use suitable stabilizing devices, e.g. bone plates with bone-screws, to fix the distance between the vertebral bodies.
Intervertebral implants are usually inserted between the adjacent vertebral body surfaces situated ventrally of the vertebral canal and so it is customary to effect the insertion of such intervertebral implants from a ventral direction. Dorsal introduction presents serious problems.
Intervertebral implants are known, which may be introduced dorsolaterally into the intervertebral space; such a vertebral body is described, for example, in DE 297 20 022 U1. In said document, however, it is not specified how, given said complicated access, the intervertebral implant is to be introduced successfully in the correct position into the intervertebral space.
The object is therefore to provide a surgical instrument, which facilitates the introduction of an intervertebral implant into the intervertebral space, especially in the case of dorsolateral introduction.
In a surgical instrument of the type described initially, said object is achieved according to the invention in that it comprises two mutually opposing guide bodies, which each have a guide directed towards the other guide body and together form between them a guideway, along which an intervertebral implant is insertable laterally into the intervertebral space.
Such an instrument may be conveyed with the two guide bodies through the body access and into the intervertebral space so that the free end of the guide bodies extends into the intervertebral space. An intervertebral implant to be inserted into the intervertebral space may then be fed forward along the guideway thus formed until the intervertebral implant passes laterally into the intervertebral space and, there, assumes the desired position exclusively through being fed forward along the guideway.
In said case, it is advantageous when the guideway in the plane of displacement extends in the shape of an arc so that the implant at the start of the guideway is introduced obliquely into the body and may then pass exactly transversely into the intervertebral space.
In a particularly preferred form of construction it is provided that the space between the guide bodies is open at least at one side along the guideway. It is therefore possible to feed the intervertebral implant forward along the guideway by means of a forward feed instrument, wherein the forward feed instrument passes through the space between the guide bodies.
It may further be provided that the guide bodies at their free end carry extensions, which are placeable against the vertebral bodies forming the intervertebral space and which are disposed next to the guideway in such a way that the intervertebral implant, which is fed forward along the guideway, at the end of the guideway next to the extension is placeable against the adjacent vertebral bodies. The extensions therefore position the guide bodies at the vertebral bodies forming the intervertebral space but are not situated in the guideway of the intervertebral implant, with the result that the latter in the course of forward feeding along the guideway lies at the end of the guideway next to said extensions and hence may leave the guideway and place itself directly against the adjacent vertebral bodies.
In particular, the extensions may take the form of prongs projecting pairwise in the direction of displacement from the end of the guideway in continuation thereof.
In a particularly preferred form of construction it is provided that the guide bodies are adjustable in terms of their mutual spacing. Thus, it is possible by means of the guide bodies, which at their free end rest against the adjacent vertebral bodies, also to spread the vertebral bodies apart so as to gain access to the intervertebral space. The guide bodies therefore perform a dual function, namely, on the one hand, the function of spreading the intervertebral space and, on the other hand, the function of guiding the intervertebral implant into the intervertebral space.
In particular, the guideway may be designed in such a way that an intervertebral implant conveyed between the guide bodies is guided in the guideway even when the distance between the guide bodies increases.
A particularly advantageous form of construction arises when the guide bodies at their opposite end to the free end are pivotally connected to one another so that a swivelling-open of the guide bodies then leads simultaneously to the spreading-apart of the vertebral bodies in the region of the intervertebral space.
In a special form of construction it is provided that each guide body comprises a flat bearing surface for the intervertebral implant and said bearing surface has laterally delimiting walls, which extend parallel to one another along the guide body and project in the direction of the other guide body beyond the bearing surface. The guideway is therefore formed by two guide bodies, which are U-shaped in cross section and surround the intervertebral implant at the top and underside and partially at the side surfaces.
It is advantageous when the guideway at its opposite end to the free end of the guide bodies exits laterally from the instrument so that an intervertebral implant is insertable into the guideway there.
In a particularly preferred form of construction it is provided that between the two guide bodies along the guideway formed by the latter a forward feed body is displaceably supported, which comprises a releasable holding device for the intervertebral implant. In said form of construction, therefore, a slide-like guide body is formed on the guideway as a driver for the intervertebral implant.
In said case, it is advantageous when the forward feed body comprises a receiving space, which is open towards thexe2x80x94in forward feed directionxe2x80x94front end of the forward feed body, for the intervertebral implant. The latter is accommodated in said receiving space, fed in said arrangement together with the forward feed body forward along the guideway and then, by retracting the forward feed body, released from the receiving space through the open side of the latter.
The receiving space may preferably be delimited by two side walls, which extend along the guideway.
In particular, it may be provided that the releasable holding device comprises elastic detent devices, which spring into recesses. The intervertebral implant is therefore held in the receiving space by a snap or detent connection, which may be released by pulling the intervertebral implant vigorously out of the receiving space.
The forward feed body at itsxe2x80x94in forward feed directionxe2x80x94rear end may comprise an access opening for a retaining element placeable on the intervertebral implant so that, after inserting the intervertebral implant, the latter may be retained in the attained position between the vertebral bodies by the retaining element when the forward feed body is retracted. In said case, the intervertebral implant exits from the receiving space of the forward feed body.
In particular, the retaining element may be curved in accordance with the guideway.
In a preferred form of construction it is provided that the forward feed body is connected to a curved forward feed rod, which is displaceable along the guideway. The connection between forward feed body and forward feed rod may in said case be releasable.
It is particularly advantageous when the forward feed rod takes the form of a toothed rack, which meshes with a toothed wheel rotatably supported on a guide body. By turning the toothed wheel the surgeon may therefore displace the forward feed rod, and hence the forward feed body and the intervertebral implant held thereon, along the guideway.
The forward feed rod may comprise a longitudinal groove for receiving and guiding a retaining element for the intervertebral implant.
In a particularly preferred form of construction it is provided that the guide bodies from their swivel bearing point up to their free end are at a decreasing distance from one another, which at thexe2x80x94in forward feed directionxe2x80x94rear insertion end of the guideway is greater than the height of the intervertebral implant and optionally the height of the forward feed body but at thexe2x80x94in forward feed directionxe2x80x94front outlet end of the guideway is smaller than the height of the intervertebral implant and/or of the forward feed body. Thus, the forward feed body and/or the intervertebral implant in the course of being fed forward along the guideway act as spreading bodies, which swivel the two guide bodies apart and hence increase the distance between the two vertebral bodies, between which the free end of the guide bodies is inserted and between which the intervertebral implant is to be inserted. The forward feed motion itself therefore leads to the spreading of the intervertebral space so that the surgeon does not simultaneously have to effect the spreading and check the forward feed along the guideway, rather the surgeon merely has to feed the intervertebral implant forward along the forward feed path and the required distance between the adjacent vertebral bodies for introduction of the intervertebral implant then arises automatically.
In said case, it is advantageous when the forward feed body and/or the guide bodies at the surfaces, which are in mutual contact, are made of a low-friction material, e.g. the appropriate surfaces may be coated with a slidable plastics material.
In another form of construction of the invention it is provided that both guide bodies are firmly connected to gripping branches, which extend beyond the hinged connecting point of the guide bodies. The end result is a forceps-like instrument, in which by pressing the gripping branches towards one another the guide bodies are swivelled apart.
It is advantageous when a stop for maintaining a minimum distance between the two guide bodies is disposed on the instrument, thereby ruling out the possibility of the intervertebral implant becoming jammed along its guideway.
The stop may preferably be adjustable so that the minimum distance may be adapted to the size of the respective implant.